This project studies the biology and behavior of free-ranging rhesus monkeys to predict their reactivity to the naturally occurring stress of leaving their natal group. In prior laboratory studies the investigators have demonstrated that monkeys with extreme asymmetric right frontal electrical brain activity chronically express excessive fearful behaviors and have increased levels of plasma cortisol and elevated cerebrospinal fluid concentrations of the neuropeptide corticotropin-releasing hormone (CRH). It is proposed that a constellation of biological and behavioral characteristics define a negative affective emotional style (fearful endophenotype) that may have long-term consequences for health. The proposed study will further characterize free-ranging rhesus monkeys' social and emotional behavior in the socially complex semi-naturalistic environment of Cayo Santiago. The purpose is to understand the biological factors associated with these dispositions, the biological similarities and differences associated with different constructs of emotional style and social status, and the effects these dispositions have on health, social functioning, and the ability to effectively deal with potentially stressful situations. The naturalistic social stressor, transfer from their natal group, that adolescent males face on Cayo Santiago provides an unprecedented opportunity to prospectively and longitudinally study relevant mediating variables over a relatively short time. The data will provide insights into the biological underpinnings of primate social and emotional behavior and how these factors confer vulnerability and resilience to stress. The data will inform human studies related to normal emotional responses, individual differences in response to stress, and the development of psychopathology.